A. Field of the Invention
This invention relates generally to the field of biological sample testing apparatus and systems, and more particularly to the subject of test sample cards which have one or more wells for containing a fluid or test sample containing a microbiological agent or organism and a reagent, and in which the well is covered and isolated from the atmosphere by a transparent membrane or tape adhered to the test sample card body to form a closed reaction chamber.
B. Description of Related Art
A variety of test sample cards are described in the patent literature which have a well or reaction site for receiving a fluid sample containing a microbiological agent, such as a microorganism, and a reagent. Several representative patents include Meyer et al., U.S. Pat. No. 4,318,994, Charles et al., U.S. Pat. No. 4,116,775; Fadler et al., U.S. Pat. No. 4,038,151 and Charles et al., U.S. Pat. No. 4,118,280, the contents of each of which are fully incorporated by reference herein. These patents describe a test sample card having a plurality of wells arranged in the test sample card body. The reagent is typically loaded in the well of the card during the completion of manufacture of the card. The reagent typically comprises a growth medium for a microbiological agent in the fluid or test sample. It is known to load a different reagent in each of the wells of the card in order to perform identification testing of a fluid sample containing an unknown microbiological agent or organism. It is also known to include in the reagent various antibiotics in order to test the microbiological agent for susceptability to the antibiotics.
In the sample testing system described in the Charles et al '280 patent, after the well of the test sample card has been loaded with the fluid sample, the card is incubated for a period of time to promote a reaction between the microorganism and the reagent, i.e., growth of the microorganism. After a period of time, the well is subject to optical analysis by a transmittance light source and a detector which are positioned on opposite sides of the well or by alternate detection methods. If the growth medium or reagent is specifically suited for or "matches up" with the particular microorganism in the fluid sample, the population of the microorganism increases substantially, or some other predetermined reaction, i.e., chemical reaction, takes place, which results in the well turning cloudy and thus having a change in light transmission characteristics. The detector determines the amount of light that is transmitted from the source through the well. By comparing the transmittance measurement over a period of time, typically several hours at least, with an initial transmittance measurement, it is possible to determine whether in fact the reagent and microbiological agent are matched by virtue of the change in transmittance measurement reaching a threshold value, such as 25 or 30 percent. The change in light transmission characteristics therefore can be used to indicate the presence of a specific microorganism in the well. Identification and susceptibility may also be detected by absorbance measurements where a fluorescent agent is provided in the growth medium.
The test sample cards described in the above patents and used in the above process have a thin transparent membrane in the form of a tape adhered to the card body covering the wells, thereby separating the interior of the wells from the atmosphere. The tape serves to prevent the fluid sample from leaking from the wells card. The tape covers the well to prevent contaminants from entering the wells. The tape also servers as a transparent window through the well, enabling light from a light source to be transmitted through the well of the card and to impinge upon a suitable detector on the other side of the well.
Several materials have been used in the prior art for the membrane or tape used to cover the sample wells. These materials include polyfluorinated polymer films such as FEP (poly(tetrafluoroethylene-co-hexafluoropropylene)) and PFA (poly[tetrafluoroethylene-co-perfluoro(alkoxy vinyl ether)], polyethylene terepthalate or PET, commonly known as Mylar, and BOPP (biaxially oriented polypropylene). All of the above materials share a common property: they are relatively impermeable to gasses and water vapor. Such materials perform adequately in terms of their functions of sealing the well and providing a transparent barrier for the well. As a result, persons working in the art have directed their efforts at improving the sample testing process by designing improvements to the test sample cards and wells themselves, improving the quality of the reagents, and improving the design of the optical instrumentation and the illumination techniques. The design and characteristics of the specific material used to cover the wells of the test sample card has been given little attention in the prior art. Whereas the prior art failed to appreciate the role that the tape can perform in improving the test reaction process, we describe herein a test sample card construction having a polymethylpentene membrane covering the wells that can substantially reduce the time required to perform the testing of the fluid sample to identify the microorganism or to determine its susceptibility to a particular antibiotic.